1. The European pipe flange standard system (i.e. PN series) represented by the European Union EN, the main standards are EN1092-1 and EN 1759 (formulated with reference to the American system).
2. The American system (i.e. Class series) represented by the American ASME, the main standards are ASME B16.5 and B16.47 (large diameter flange).
In addition, there is the Japanese JIS system (the nominal pressure is represented by K), but it basically follows the American system.
1. National standard GB;
2. Chemical industry standard HG;
3. Machinery industry standard JB;
4. Petrochemical industry standard SH.
